foraminifera: an amoeba with a shell

from guest contributor Howard Allen . . .

I LOVE forams! Their biggest appeal to me is their stunning diversity of forms. The smallest ones are dust-particle sized, while the largest can be nearly the size of a frisbee (see Guiness Book of Records under "largest protozoan"). A more typical size is like a grain of sand.

You can think of foraminifera (forams for short) as "an amoeba with a shell". They are classified on the basis of the composition and structure of their shells. One group has shells made up of particles of silt or sand that are glued together by the foram animal. Some of these little guys can even select particular mineral types from the sediment to make their shells: magnetite, quartz, mica, diatom shells, sponge spicules, etc. How 'bout that for a single-celled organism! Another group makes its shells of opaque white calcite that looks for all the world like fine bone china. Another group uses transparent (sometimes colored) calcite that looks like glass.

The diversity of shell shapes is mind-boggling. One critter, Lagena, has a shell that looks like an elegant, fluted glass bottle or vase. Some look like miniature ammonites. Some look like bunches of grapes. Some look like strings of beads. Some look like bananas with ribs. Some form straight tubes. Some have multiple chambers inserted at precise angles. Some look like stars. Some look like rice grains. Some look like lentils. Some are attached to the sea-bottom like little trees. The variety is endless.

The geological range of forams is very long. The oldest ones are (I think) Ordovician, and they are very common in today's seas. They are almost exclusively marine (sea water), but some are tolerant of or prefer higher or lower salinities. They are also sensitive to water temperature, depth, energy level (calm water, pounding surf).

The only real limiting factor in collecting them is that you need a microscope, preferably a binocular dissecting scope, with magnification in the range of 10x to 50x. Many of these are available for a few hundred dollars or even less for used 'scopes.

You can find forams in all sorts of sediment. The easiest way is to simply grab a vial of sand from an ocean beach and look at it under the microscope. Tropical beaches, especially those near coral reefs (Florida, Caribbean, Mexico, South Pacific islands), tend to have more and larger forams than cooler water beaches, and muddier sediment tends to have more forams than coarser sand sediment. Bermuda's famous pink sand beaches are colored by billions of red and pink forams. Planktonic (floating) forams can be collected by dragging a very fine net behind a boat. I have obtained wonderfully rich collections of forams from gobs of mud brought up on a ship's anchor in the Arctic Ocean. I ask my friends (especially those who snorkel or scuba dive) to bring me back pill bottles or film cans or small zip-lock bags with sediment from their holidays. One person brought me a bottle of sediment from the Egyptian pyramid of Cheops that was full of fossil forams (Eocene). Turns out that the pyramids were built of limestone that is chock-full of big, lentil-shaped forams. I have rice-grain sized Pennsylvanian-age forams (fusulinids) weathered loose from limestone in Texas. I have collected similar, Permian-aged forams in the mountains of central British Columbia. Chalk and marl beds are a great source of foram fossils. I have seen beautiful forams in rock cuttings from deep in oil and gas wells I've worked on in Canada and Costa Rica.

Google "foraminifera" to find photos and more information on the web. The "bible" for foram enthusiasts is Part C (2 volumes) of the Treatise On Invertebrate Paleontology, which is available at bigger libraries (especially university libraries). Have fun!